Thermostatic snap-acting switch



March 4, 1969 H. D. EPSTEIN THERMOSTATIC SNAP-ACTING SWITCH Filed Dec. 50, 1966 2.2

United States Patent 3 Claims ABSTRACT OF THE DISCLOSURE A dished, bimetal plate is mounted as a cantilever beam, being fixedly connected on one side of its dished portion to a base and carrying a movable contact on its free end on the opposite side of said dished portion. The movable contact is engageable and disengageable with a fixed contact on the base. A resilient tongue is struck out from the dished portion intermediate the fixed end of the plate and said contact. An adjustable fixed means engages the tongue to cause the latter to force the plate toward engagement of its movable contact with the fixed contact. The fixed contact and the metal of high coefficient of expansion are on the concave side of the dished portion of the plate so that upon heating thereof by flow of current therethrough or in response to change in ambient temperature, the plate will snap to an open position wherein said contacts are separated.

Among the several objects of this invention may be noted the provision of a thermally responsive snap-acting switch of the dished-plate, single-break type which by improved and simple means can be adjusted for contact pressure minimizing its creep action and controlling its operating temperatures; and the provision of such a switch having more sensitive calibrating means for more closely obtaining the contact pressure desired. Other objects and features will be in part apparent and in part pointed out hereinafter.

The invention accordingly comprises the constructions hereinafter described, the scope of the invention being indicated in the following claims.

In the accompanying diagrammatic drawings, in which several of various possible embodiments of the invention are illustrated,

FIG. 1 is a side elevation partly in section of one form of switch made according to the invention;

FIG. 2 is a plan view of the thermally responsive member of the FIG. 1 switch;

FIG. 3 is a view similar to FIG. 2 showing a modified form of the thermally responsive member;

FIG. 4 is a view similar to FIG. 1 showing another embodiment of the invention; and

FIG. 5 is a fragmentary plan view of a part of the FIG. 4 form of switch.

Corresponding reference characters indicate corresponding parts throughout the several views of the draw- 1ngs.

Referring to the drawings, numeral 1 indicates an insulating base plate. A contact 3 is mounted on a terminal 5 attached to base 1. Another contact 7 is mounted on a terminal '9.

A springy bimetallic thermally responsive sheet or strip generally designated 11 in FIG. 2 has an end portion 13 which is secured to the upper surface of contact 7. The strip also has an extending portion 15 and an end portion 17 which carries a contact 19. The strip comprises a layer of metal of a comparatively high thermal coefficient of expansion on its lower side (as viewed in FIG. 1) and a layer of metal with a lower thermal coefficient of expansion on its upper side. Because of the thinness of the "ice strip 11, the two layers are not indicated on the drawings. Strip 11 is upwardly dished as indicated at 18 so that it snaps when it moves between the solidand dotted-line positions shown in FIG. 1. When the strip is cool it is in the position shown by the solid line in FIG. 1. Upon heating it to a predetermined critical temperature, the greater expansion of the lower layer of metal relative to the upper layer of metal causes the strip to snap upward to the FIG. 1 dashed-line position. Thereafter on cooling of the strip to another predetermined critical temperature the strip will snap back to the solid-line position. The contact 19 is in electrical engagement with the contact 3 when strip 11 is in the solid-line position, thereby completing an electrical circuit from terminal -5 through contacts 3 and 19, then through the strip 11 and contact 7 to the pin 9. This circuit is broken when the strip snaps to the dashed-line position. As the drawings show, the member 11 is mounted as a cantilever beam.

A springy or resilient tongue 21 is struck from the portion 15 of the strip, leaving hole 23 (FIG. 2). The tongue extends lengthwise of the strip.

Bearing against the tongue 21 is a rivited part 22 located in a finger 25 at one end portion of an adjustment member 27. The part 22 is composed of insulating material so that member 27 carries no current. There are other Ways in which to accomplish this, as will be clear to those skilled in the art. For example, member 27 may be mounted on the insulating base 1 instead of on contact 7. Member 27 has an end portion 29 which is secured to the strip 11 above contact 7. The finger 25 is joined to portion 29 by a bendable, nonspringy arm 31. Arm 31 can be bent to move finger 25, including part 22, toward or away from the tongue 21 so as to increase or decrease the pressure thereon. Thus the member constituted by arm 31 and finger 25 is also mounted as a cantilever beam.

Assuming that contact 19 touches contact 3, the pressure exerted by finger 25 through its end part 22 on tongue 21 is transmitted through the springy tongue 21 to the strip 11. Strip 11 becomes mechanically stressed while increasin the contact pressure between contacts 3 and 19. When the temperature of bimetallic strip 11 is raised either by an increase in ambient temperature or by the passage therethrough of electrical current (1 R heating), the free end of the strip tends to creep upwardly, as seen in FIG. 1, prior to snapping as described supra. The free end of tongue 21 is attached to strip 11 and also composed of 'bimetal, and would therefore tend to move upwardly in like manner. Part 22, however, biases the tongue downwardly which increases the net forth between contacts 19 and 3. By thus restraining the movement of tongue 21 some or all so-called creep action between the contacts which would otherwise tend to open the contacts upon heating before snap action would occur is offset and eliminated. It also serves as a means for determining the temperature at which snap action will open the switch. As the arm 31 is bent counterclockwise, the contact pressure increases as the member 15 is stressed, with the result that creep action before snap is increasingly removed and the temperature lowered which causes snap action to the dotted-line position (FIG. 1). Thus the opening temperature of the switch can be adjusted while eliminating creep by bending the arm 31 toward or away from the strip to increase or decrease the spring pressure exerted by the end part 22 of finger 25. An additional advantage of employing the tongue 21 for transmitting force to the member 15 is that the tongue itself, during the time that it is struck out from member 15, may be set in position to vary the parameters for the operating temperature and removal of creep.

A modified form of the strip is illustrated in FIG. 3. This strip is generally designated 33 and is the same as the strip 11 previously described except that the tongue 35 projects toward the contact 19 instead of away from it as in FIG. 2.

Another embodiment of a switch of the invention is illustrated in FIGS. 4 and 5. In this embodiment the dished bimetallic strip is designated 39 and is similar to the strip 33 shown in FIG. 3, except there is a hole or passage 41 formed through a tongue 43 while the tongue is shown projecting toward the end of the strip containing the contact 19, it will be understood that it can also extend in the opposite direction if desired.

An adjusting screw 45 has a shank portion which is passed through hole 41 and screwed into the base 1 of the switch. The head 47 of the screw is somewhat larger in diameter than the hole 41 in the tongue so that the screw can be adjusted downward until the head exerts pressure against the tongue. A coil spring 49 surrounding the shank portion of the screw reacts from base 1 against tongue 43 to bias the tongue against the screw head. When screw 47 is driven down to exert pressure against tongue 43, the results are like those above described.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A thermostatic switch comprising a dished bimetal plate in the form of a cantilever beam fixedly mounted on one side of its dished portion and carrying a movable contact at its free end on the other side of said dished portion, a fixed contact engageable by said movable contact, a resilient tongue struck from said plate within the area of its dished portion, and means engaging the tongue to apply a resilient force by the tongue to the plate to press the movable contact toward engagement with the fixed contact when the contacts are closed.

2. A switch made according to claim 1 wherein said fixed member engaging the tongue is in the form of a bendable cantilever beam for adjustment of pressure on the tongue.

3. A switch made according to claim 1 wherein the tongue includes a passage therethrough and said means for engaging the tongue is in the form of a screw having a head and extending through the passage for adjustment of pressure on the tongue by said head, and a spring holding the tongue against said head.

References Cited UNITED STATES PATENTS 2,820,870 1/1958 Moksu 200-113 2,892,910 6/1959 Diebold 200-113 3,067,306 12/ 1962 Epstein 2001 13 FOREIGN PATENTS 1,102,506 5/1955 France.

BERNARD A. GILHEANY, Primary Examiner.

R. COHRS, Assistant Examiner.

US. Cl. X.R. 

